RemoteCommands and SendClearCache plugins for MODX Revolution 2.2+

plugin.RemoteCommands.php

<?php
/* RemoteCommands plugin -- register with OnHandleRequest OR OnWebPageComplete event */

/* define the IP of the master instance which does not need to execute remote commands */
$master_instance = $modx->getOption('master_instance', $scriptProperties, '127.0.0.1');

/* get the instance IP */
$instance = $_SERVER['SERVER_ADDR'];

/* the number of seconds the remote command is valid for */
$seconds = !empty($seconds) ? intval($seconds) : 1440;

/* find any remote commands to execute from the master instance */
if (!empty($instance) && $modx->getService('registry', 'registry.modRegistry') && $instance !== $master_instance) {
    $modx->registry->addRegister('remotes', 'registry.modDbRegister', array('directory' => 'remotes'));
    $modx->registry->remotes->connect();

    /* if not already registered, register this instance for $seconds */
    $modx->registry->remotes->subscribe("/distrib/instances/{$instance}");
    $registration = $modx->registry->remotes->read(array('poll_limit' => 1, 'msg_limit' => 1, 'remove_read' => false));
    $modx->registry->remotes->unsubscribe("/distrib/instances/{$instance}");
    if (empty($registration) || !reset($registration)) {
        $modx->registry->remotes->subscribe("/distrib/instances/");
        $modx->registry->remotes->send("/distrib/instances/", array($instance => "{$instance}"), array('ttl' => $seconds));
        $modx->registry->remotes->unsubscribe("/distrib/instances/");
    }

    /* find any valid command messages for this instance and act on them */
    $modx->registry->remotes->subscribe("/distrib/commands/{$instance}/");
    $commands = $modx->registry->remotes->read(array('poll_limit' => 1, 'msg_limit' => 1));
    $modx->registry->remotes->unsubscribe("/distrib/commands/{$instance}/");
    if (!empty($commands)) {
        $command = reset($commands);
        if (!empty($command)) {
            /* customize this with your own command handlers */
            switch ($command) {
                /* refresh the remote instance's cache */
                case 'clearCache':
                    switch ($modx->event->name) {
                        case 'OnHandleRequest':
                            $modx->reloadConfig();
                            $modx->reloadContext();
                            break;
                        case 'OnWebPageComplete':
                            $cacheRefreshOptions =  array(
                                'auto_publish' => array( 'contexts' => array('web') ),
                                'system_settings' => array(),
                                'db' => array(),
                                'context_settings' => array( 'contexts' => array('web') ),
                                'scripts' => array(),
                                'resource' => array( 'contexts' => array('web') ),
                                'default' => array(),
                            );
                            $results = $modx->cacheManager->refresh($cacheRefreshOptions);
                            break;
                    }
                    break;
                case 'clearErrorLog':
                    /* empty the remote instance's error.log */
                    $modx->cacheManager->writeFile($modx->getCachePath() . 'logs/error.log', '', 'wb');
                    break;
                default:
                    break;
            }
        }
    }
}

plugin.SendClearCache.php

<?php
/* SendClearCache plugin -- register with OnSiteRefresh event */

/* seconds property defines a default ttl value for the clearCache message [default=1440] */
$seconds = !empty($seconds) ? intval($seconds) : 1440;

/* number of seconds to delay the clearCache message before it should be executed [default=0] */
$delay = !empty($delay) ? intval($delay) : 0;

/* number of seconds to stagger the clearCache messages between instances [default=5] */
$stagger = !empty($stagger) ? intval($stagger) : 15;

/* read instances and write clear cache msg to each command directory */
if ($modx->getService('registry', 'registry.modRegistry')) {
    $modx->registry->addRegister('remotes', 'registry.modDbRegister', array('directory' => 'remotes'));
    $modx->registry->remotes->connect();
    $modx->registry->remotes->subscribe('/distrib/instances/');
    $instances = $modx->registry->remotes->read(array('poll_limit' => 1, 'msg_limit' => 200, 'remove_read' => false));
    $modx->registry->remotes->unsubscribe('/distrib/instances/');
    if (!empty($instances)) {
        $staggerCurrent = 0;
        foreach ($instances as $instance) {
            if ($instance == $_SERVER['SERVER_ADDR']) continue;
            $modx->registry->remotes->subscribe("/distrib/commands/{$instance}/");
            $modx->registry->remotes->send("/distrib/commands/{$instance}/", array('clearCache'), array('ttl' => $seconds, 'delay' => $delay + $staggerCurrent));
            $modx->registry->remotes->unsubscribe("/distrib/commands/{$instance}/");
            $staggerCurrent = $staggerCurrent + $stagger;
        }
    }
}